Doc Magnus unsuccessfully attempts to repair Platinum's faulty responsometer when his therapist Isobel Sullivan arrives with Mona Bennet, who needs help with her fiancé Dr. Bruce Gordon. Bennet reveals that Gordon transforms involuntarily into the villain Eclipso whenever exposed to any eclipsed light, due to a wound from a black diamond. After a failed attempt to destroy Eclipso permanently, Gordon discovered a letter leading him to Germany in search of mysterious documents from a lost Peruvian city dating back to the 1500s. Magnus and the Metal Men travel to Germany where they confront Eclipso at a university library, leading to a battle and the discovery of a map to the Peruvian Andes.
